Matthew Archer (Jet Propulsion Laboratory, California Institute of Technology, USA); Patrice Klein (Jet Propulsion Laboratory, California Institute of Technology, USA); Lia Siegelman (Scripps Institution of Oceanography, UCSD, USA); Andrew Thompson (Caltech, USA); Dimitris Menemenlis (San Jose State University, USA); Lee-Lueng Fu (Jet Propulsion Laboratory, California Institute of Technology, USA); Jinbo Wang (Texas A&M University, USA)

Satellite observations using advanced wide-swath altimetry reveal, for the first time, that mid-latitude oceans are densely populated with cyclones spanning 5–10 km in size. These features, called submesoscale cyclones, are significantly smaller than the well-known mesoscale eddies (50–-200 km) and are associated with intense surface geostrophic currents reaching up to 1 m/s. They exhibit spin rates on the order of a few hours, much shorter than the multi-day timescales typical of mesoscale eddies. Despite arising from distinct physical mechanisms, these compact cyclones display remarkable structural and dynamical similarities to atmospheric hurricanes.
Leveraging a numerical model with unprecedented spatial resolution over a large domain in the Western Pacific, we show that these numerous submesoscale cyclones emerge from instabilities within strongly sheared mesoscale currents. They are associated with vertical velocities exceeding 500 m/day at a depth of 40 m, driving upward heat fluxes surpassing 800 W/m^2 in the upper 200 m of the ocean. Through their vigorous vertical motions, this widespread population of submesoscale cyclones is expected to play a crucial role not only in upper-ocean dynamics and air–sea exchanges, but also in carbon sequestration and nutrient redistribution, thereby shaping marine ecosystems and potentially influencing the climate system